1. Field of the Invention
The present invention relates to a process and associated treatment reagents for use in the natural gas exploration industry, and more specifically to a means for converting intractable, semi-solid, drill cutting wastes from gas well development to granular, free-flowing Stabilized Drill Cuttings, termed “SDC material,” which is an environmentally compliant product that can be used, in compacted form, for many beneficial applications in engineering construction as a replacement for naturally occurring mined and/or quarried minerals.
2. Description of the Prior Art
Exploration wells to recover natural gas from deep deposits of black shale throughout Appalachia (Marcellus, Utica, etc), Colorado, Utah, Wyoming, Texas, etc., are a major new source of clean energy for the US economy, with enormous growth being projected over the next ten years.
As a by-product of the gas exploration process, approximately 10,000 tons, or more, of intractable drill cuttings may be produced as semi-solid, mud-like wastes (FIG. 1) from one exploration site alone. When hundreds, or thousands, of such exploration sites are considered, this represents a huge volume of waste material which must be managed in an environmentally sound manner.
The drill cuttings are considered by regulatory authorities as waste, which requires their disposal in controlled, engineered landfills at substantial costs to the industry, both in trucking costs and disposal (tipping) fees. Prior to such disposal, the semi-solid, wet drill cuttings must also first be dried/dewatered to the extent that they pass the EPA Method 0905B Paint Filter Liquids Test. This treatment, typically conducted by adding quicklime (CaO) to the wet drill cuttings, must be conducted at the well development site prior to trucking to the disposal site.
Drill cuttings from gas well exploration are typically extremely fine grained, where 90% or more of the material is finer than 50 mesh or 300 μm (FIGS. 2 & 3). Two distinct types of cuttings are produced from a single gas well: vertical cuttings and horizontal cuttings. The vertical cuttings vary from location to location and are typically comprised of a wide range of rock and mineral types including limestone, dolomite, and sandstone, The horizontal cuttings are typically comprised of gas-bearing shale inter-bedded with other mineral/rock types including quartz, calcite, dolomite, muscovite, and anorthite (FIG. 4). The vertical cuttings are largely produced with water as the drilling lubricant. The horizontal cuttings, which constitute by far the majority of the drill cuttings from a given site, typically contain, in addition to water, various oils and other additives used for lubrication and rheological control. Both forms of cuttings are produced and brought to the surface with high moisture content, typically in the range 10% to more than 45%, as an intractable, semi-solid, mud-like material which is very difficult to handle.
It will be appreciated that, overall, the management of the drill cuttings has a significant negative impact on the gas exploration industry, not only on the economics of operations, but also on the environmental sustainability. As noted above, the current practice by the industry is to treat the intractable drill cuttings with a drying agent, such as quicklime, to pass the EPA Paint Filter test. The treated drill cuttings are then trucked off-site for disposal at a landfill, which may be a considerable distance from the exploration site. This practice creates considerable pressure on the capacities of landfills in the region, together with the associated heavy truck traffic on local roads. In addition, the quicklime used for the drying process has a substantial carbon footprint, in that approximately one ton of the greenhouse gas carbon dioxide is released during the manufacture of one ton of lime. This means that for a single exploration site alone which produces 10,000 tons of drill cuttings during the well development phase, the lime treatment releases the equivalent of approximately 2,000-3,000 tons of carbon dioxide to the atmosphere. To improve the sustainability of the gas exploration process, it is therefore highly desirable that means be developed to beneficially use the waste drill cuttings and thereby reduce or preferably eliminate the need for disposal, together with the associated environmental and economic penalties.
In order to solve this problem, a process has been developed as disclosed in U.S. Pat. No. 8,007,581 in which drill cuttings are mixed with various binders in order to form material for use in drilling pads and vehicle roadways at alternate drill sites normally 5-10 miles away. In such an application, the drill cuttings are processed on the current drill site and transported to the new drill site.
Depending on the existence and types of aquifers at the location of the drill site, the water content of the drill cuttings can vary between 10% and 80%. Since the material strength of the material is a function of the ratio of the water to binder content, the amount of binder to be added to the drill cuttings varies as a function of the water content. As such, the cost for forming the drill cutting into a useable construction material is unstable and can vary substantially. In addition. construction materials formed from drill cuttings with a relatively high water content are relatively expensive to store and transport. These costs can approach the cost of transporting and dumping untreated drill cuttings to a landfill.
Another problem with known technology, such as disclosed in the '581 patent, relates to the process for forming a load bearing structure. The '581 patent teaches a process of adding a sufficient amount of pozzolanic binder or asphalt to the drill cuttings to form a cementitious mixture in order to form a load bearing structure. Unfortunately, using the drill cuttings as an aggregate to a pozzolanic binder or asphalt requires that the load bearing structures be formed at another drilling site prior to the completion of the drilling at the existing drill site. This process is somewhat cumbersome and further adds to the cost of using the drill cuttings for an engineering construction application which further drives the cost toward the cost of disposal of such drill cuttings.
Thus, there is need for utilizing the drill cuttings for useful construction applications, such as drill pads and roadways with relatively stable costs.